The present invention relates generally to capacitors and more particularly to systems and methods for the fabrication of titanium and titanium alloy anodes for dielectric and insulated films.
Titanium and titanium alloy anodes have an advantage in energy density (J/g), cost ($/g) and material density (g/cm3) when compared with tantalum and niobium anodes. Further, titanium is capable of providing a higher capacitance·voltage per gram (CV/g), for example, the gain is up to 10 times that of tantalum. Thus, a capacitor fabricated with a titanium or titanium alloy anode is physically smaller or, alternatively, a like sized component, possesses a higher capacitance rating than that fabricated with tantalum. When titanium or a titanium alloy is used instead of tantalum in capacitor fabrication in a capacitor having similar performance specifications, material costs are also greatly reduced, by as much as 100 times.
While titanium fabrication is advantageous, physical characteristics of the metal have heretofore prevented widespread adaptation. The structure, crystallization kinetics, and composition, as well as the electrical and electrochemical behavior, of an anode film on titanium or a titanium alloy are somewhat contradictory and inconsistent in nature. Moreover, these phenomena are mutually and multifariously related during anodizing. Further, the insulating and dielectric behavior of the anode film, e.g., leakage current and capacitance, are uncertain and inconsistent irrespective of the electrochemical parameters, including voltage, current, chemistry, concentration of electrolyte, heat treatment, and the like. As a result, titanium and titanium alloys have generally been disqualified from use in capacitors, save in possible exceptions metal for certain metal capacitors.
Thus, there exists a need resolve the inconsistent capacitance and the high and variable leakage current behaviors associated with the use of titanium and titanium alloys for anodes. Furthermore, there exists a need for controlling leakage current and capacitance in the processing or manufacture of capacitors using titanium and titanium alloy anodes. Also, in order to use titanium or a titanium alloy as a capacitor anode, the origin of the inconsistency and variation in the electrical behavior of the anode film must be understood. Moreover, the critical factors in processing or manufacture should be clearly defined. Thus, there exists a need for a new fabrication technique for anodes using titanium or a titanium alloy. Low equivalent series resistance (ESR) and high heat dissipation are also generally desired.